The demand for at-home and point-of-care medical diagnostics tools is on the rise. A number of diagnostic tools exist to quantify and analyze biological cells or molecules in a sample. In accordance with one conventional technique, commonly referred to as magnetic labeling, magnetic nanoparticles (labels) are caused to bind to the target molecules, such as DNAs or protein, undergoing analysis. Integrated biosensors designed to operate based on the magnetic labeling principle dispense with costly optics and thus are less expensive than systems that use fluorescence for bio-molecular detection.
However, despite their relatively higher sensitivity and lower cost, conventional magnetic biosensors measure changes in the magnetic susceptibility either at low frequencies or at a fixed radio frequency (RF), and thus do not differentiate between a large number of small magnetic particles and a smaller number of larger magnetic particles containing a similar magnetic content.